1. Field of the Invention
The present invention relates to a process and apparatus for forming a product of a thermoplastic material. More particularly, the present invention pertains to a process and apparatus for manufacturing a product made of a thermoplastic material by placing a pair of sheets of a thermoplastic resin between a pair of molds and injecting pressurized gas between the pair of thermoplastic resin sheets so that the sheets are deformed under the gas pressure along the mold cavities.
2. Description of the Prior Art
Known processes for manufacturing a thermoplastic resin product includes a so-called blow molding in which a pair of resin sheets are placed between a pair of molds and pressurized gas is introduced between the sheets to form the sheets along the forming surfaces of the molds. In the case where the blow molding is applied to a forming of a thermoplastic resin, the molds may be mounted on a hot press machine so that the molds are heated during the forming process. Alternatively, the molds may be provided with heaters which are embedded therein and the forming process may be carried out in a press machine.
In the conventional processes, the molds are forced toward each other by means of a press only in one direction. Therefore, the processes can be applied for a manufacture of a product having relatively planar mating surfaces. Another problem inherent to the conventional processes is that the molds used in these processes must be of precisely machined ones so that they can be used in a press machine. It should further be noted that there is a limit in the conventional processes in respect of the size of the products made by these processes since the processes must be carried out in press machines. A further problem in the conventional processes is that the part halves produced by the pair of resin sheets are not attached together at the time of molding so that they have to be joined together after the molding process.